1. Field of the Invention
The present invention relates to a light-emitting diode lighting circuit. More particularly, to a light-emitting diode lighting circuit which can prevent the light-emitting diode from being erroneously illuminated due to leakage or the like of a switch which instructs the light-emitting diode to illuminate.
2. Description of Background Art
An example of a conventional light-emitting diode lighting circuit is shown in FIG. 2. In FIG. 2, light-emitting diodes (hereinafter, referred to as “LEDs”) 1, 2 and 3, and resistors 4, 5 and 6 serially connected to the LEDs 1, 2 and 3, respectively, are connected to a battery 11 through a switch 7. By closing the switch 7, current flowing through the LEDs 1 to 3 and the resistors 4 to 6, and the LEDs 1 to 3 are illuminated.
It is preferable that the LEDs 1 to 3 are not illuminated when the switch 7 is opened. Nevertheless, the LEDs 1 to 3 sometimes remain illuminated due to leakage even though the switch is opened. This is because impedances are high in LEDs.
Therefore, it is considered that lighting when the switch is opened is prevented by connecting separate resistors, besides the resistors 4 to 6, to the LEDs 1 to 3 in parallel to substantially reduce the impedances of the LEDs.
Moreover, a circuit is known which includes a constant current source circuit in order not to change current flowing in the LEDs even though a voltage applied to an LED drive circuit changes as set forth in Japanese Patent Laid-Open Publication No. Heisei 1-123483.
In the example wherein the resistors are connected to the LEDs in parallel, resistance values of the connected resistors have to be reduced to a leakage resistance value of the switch 7 (80Ω, for example). Therefore, an apparent load is increased. Further, large-capacity resistors are required to prevent heating. Therefore, flexibility in layout is reduced, and the costs is increased. Meanwhile, as for the example in which a constant current source circuit is provided, the circuit becomes complicated, and the costs are likely to be increased.
Therefore, it has been demanded to prevent erroneous lighting of the LEDs with a relatively simple circuit.